None.
Not applicable.
1. Field of the Invention
The preferred embodiments of the present invention are directed generally to systems having multiple power supply units, with each power supply unit responsible for supplying some portion of the electrical current to the load. More particularly, the preferred embodiments are directed to increasing the accuracy of the current sharing signal that extends between the power supply units to ensure that each power supply unit carries a proportionate amount of the load.
2. Background of the Invention
It is common in the design of electronic systems, especially systems that need redundancy, to provide multiple power supply units. In normal operation, the load is split between two or more power supply units; however, in the event that one power supply unit fails, the remaining power supply unit (or units) provides the additional power to keep the system operational. FIG. 1 shows, in block diagram form, a related art system having two power supply units 10 and 12 supplying power to an exemplary load 14. In particular, FIG. 1 shows that each of the power supply units 10, 12 has a power supply 16 and 18 respectively. This power supply converts the incoming power, which may be an alternating current (AC) or direct current (DC) signal, into an appropriate, typically DC, source for use by the load 14. Each power supply unit has a diode 20, 22 to prevent electrical current from one power supply unit from flowing in reverse fashion into a second power supply unit.
In order to balance the load carried between multiple power supply units in a system, it is necessary to measure the output current of each individual power supply unit 10, 12. In the related art, this is done by a low value series resistor 24, 26 in series with the output of the power supply unit 10, 12. Current flowing through the series resistor 24, 26 develops a differential voltage, which is indicative of the overall power supplied by each power supply unit 10, 12. The differential voltage is fed to a load control unit 28, 30, which converts the differential voltage into a current sharing signal that is coupled to other power supply units by way of the load control line 32. Each power supply unit 10, 12 monitors the current sharing signal on the load control line 32, and adjusts its output voltage (and therefore its output current) in an attempt to level the load between the various power supplies.
FIG. 2 shows a related art load control unit. In particular, the differential voltage from the series resistor feeds an amplifier 34, which takes the differential signal and creates a voltage proportional to the differential voltage. The Intelligent Platform Management Interface (IPMI) standard, a specification created by a conglomerate of computer manufacturers, requires that the current sharing signal range from zero to eight volts as the power supply unit power output ranges from zero to full load. The output of the amplifier 34 feeds through an isolation amplifier 36 to the load control line 32. Consider, for purposes of explanation, that another power supply unit is supplying more of the total required power than the power supply unit in which the load control circuit of FIG. 2 resides. In this case, the voltage at the output of the amplifier 34 is lower than the voltage on the voltage control line 32. The difference is sensed by the combination of isolation amplifier 38 and circuit 40, and is fed to a power supply voltage control unit (not shown).
Because of electrical noise, resistive shot-noise, imperfections in amplifier manufacturing, and the like, the internal current sharing signal 42 may not accurately reflect the load carried by the power supply unit, especially DC offsets in the signal not attributable to current flow. There are two related art approaches to addressing, though not solving, this problem. The first is to adjust the gain of the load control unit such that at fall load the current sharing signal 42 accurately reflects the output power. This, however, may create substantial errors at the low supplied-power end, e.g. at the 50% load, where power supply units operate in a two-power supply unit configuration. The second approach is to adjust the internal current sharing signal 42 to accurately match actual supplied power at the mid-range (or some other relevant loading), but this method too induces error both at the higher and lower ends of the supplied power spectrum. The IPMI specification allows for as much as a 10% difference in load carried among parallel supply units.
Thus, what is needed in the art is a system and related method for accurately detecting and generating the current sharing signal for more precise load sharing in multiple power supply situations.
The problems noted above are solved in large part by a system and related method that compensates for the errors in creation of the current sharing signal. More particular, the preferred embodiments are directed to a circuit which reads the differential signal created by the series resistor, and creates a current sharing signal, which is adjustable not only with respect to its gain, but also with respect to its offset. In a second aspect, the preferred embodiments are directed to a method of calibrating the load control circuits of power supply units with a computer that involves first setting the gain of the load control circuit, followed by setting the offset of the load control circuit.
The disclosed devices and methods comprise a combination of features and advantages which enable it to overcome the deficiencies of the prior art devices. The various characteristics described above, as well as other features, will be readily apparent to those skilled in the art upon reading the following detailed description, and by referring to the accompanying drawings.